The invention relates to a setting drive or servo drive for the conformal positioning of a take-off shaft. It has a reducing spindle drive, one part of which is axially fixed but turnable and drivable. The other part thereof engages a torsion-resistant and longitudinally movable band or flexible tension member the first mentioned part. One end of the flexible low-expansion tension member is fastened under pretensioning on the longitudinally movable part of the spindle drive and the other end thereof is torsionally connected with the take-off shaft.
Setting drives of this type have many possibilities of use. They serve, for instance for follow-up of readings or for the motion of robot members.
The setting drive mentioned in the beginning is known from U.S. Pat. No. 3,614,898 and consists of a spindle, which on the end side is axially fixed but turnable, and of a nut which is axially movable by rotation of the spindle and on whose axial ends there are fastened bands consisting, for instance, of phosphor bronze.
The other ends of the bands crossing each other are fastened adjustable and therefore pretensionable on the peripheral surface of a curve segment which itself is fastened on the take-off shaft extending vertical to the spindle axis.
As far as the curve segment of this well-known setting drive, as illustrated, is a circle segment, the pretensioning set in a certain initial position and thereby the freedom from play between nut and take-off shaft during the rotation of the spindle (this during the operation of the setting drive) does not remain preserved because the geometric relations change. In order to take this into account, a complicated curve structure would be needed which again makes impossible a motion of the take-off shaft over more than a relatively small angle of traverse.
Above all, however, in connection with the well-known setting drive the pretensioning of the bands relative to the nut does not permit the equalization of play between the spindle and the nut. But the elimination of this play is of decisive importance because it has a considerable influence on the accuracy of the transfer of motion.